The present invention regards a method of the type indicated in the preamble of the attached claim 1. A method of this type is disclosed in SU 894 923 A1. Methods for forming nanoporous polymeric membranes without the use of a mask are disclosed in EP 1 849 516 A1 and in R.SPOHR, “Radiation measurements”, vol. 40, 20 May 2001, pages 191-202. The use of a mask in the heavy ion irradiation of polymeric carriers, for producing holes which do not pass through the carrier, is disclosed in US 2005/230353 A1 as well in Yousef H. et al., “Ion track enabled multiple wire microvia interconnects in printed circuit boards” (from “Nuclear Instruments % methods in Physics Research”, Section B: “Beam Interactions with Materials and Atoms”, Elsevier, Amsterdam, NL—DOI: 10, 1016/J. Nimb. 2007.11.014, vol. 266, no. 8, 1 Apr. 2008 (2008-04-01), pages 1659-1665, XP022658868, ISSN: 0168-583X) and in Metz S. et al., “Polyimide microfluidic devices with integrated nanoporous filtration areas manufactured by micromachining and ion track technology” (from “Journal of Micromechanics & Microengineering, Institute of Physics Publishing, Bristol GB LNKD-DOI: 10.1088/0960-1317/14/3/002, vol. 14, no. 3, 1 Mar. 2004, pages 324-331, XP020069627 ISSN: 0960-1317).
The production of nanoporous polymeric membranes with high-aspect-ratio nanopores (i.e a value exceeding at least 10, and preferably exceeding 100, of the ratio between an axial dimension and a transverse dimension of the nanopores) and wherein the nanopores form a highly ordered arrangement, represents a technological problem yet to be solved.
The possible applications of this type of material are numerous and varied. The need for these materials lies in their possible and immediate use in existent systems and devices among which: lithium batteries separators, polymer fuel cells, filtering systems, membranes for microfluidic systems, and as an element for enabling manufacturing other nanostructured objects (nanowire sensors, nanostructured electrodes for solar cells and planar optoelectronic devices), nanostructured particles, materials made of nanocomposites and artificial metamaterials, etc.
Currently, it is possible to obtain nanoporous membranes by means of a process that provides for bombing polymer films with high energy focused heavy ion beams which degrade the material breaking the chemical bonds along the path of the ions. Subsequently to the bombing step, through a chemical etching process, it is possible to remove the material starting from the degraded zones and obtain through pores which pass through the polymer film (“Track-etched membranes”). Regarding this see R. Spohr, Radiation Measurements, Volume 40, 2005, pages 191-202.
Given that the accelerated ions are propagated in a beam typically through the Gaussian process, the method described above characteristically allows producing a random arrangement of through nanopores in polymer layers (for example PC, PA, PP, PBI, PVDF, PEEK, PMMA, PTFE).
The attached FIG. 1, extracted from the article “Nanoporous β-PVDF membranes with selectively functionalized pores”, O. Cuscito, M. C. Clochard, S. Esnouf, N. Betz, D. Lairez, Nuclear Instruments and Methods in Physics Research B265 (2007) pages 309-313, shows an example of a membrane obtained through a method of this type.